The present invention relates to an efficient lighting system which provides both normal and emergency lighting throughout a facility.
Electrical codes, both state and national, require that certain public places, for example schools, restaurants, hospitals and work places, have emergency lighting which is activated automatically in the event of a power failure. There are generally two main types of emergency lighting systems in common use, i.e., the individual unit and the Central Inverter System ("CIS"). The individual unit light is basically a set of floodlights connected to a battery. A charging and sensing circuit in the unit is connected to the standard a.c. power line and uses it to keep the battery charged, as well as to detect a power failure. When a power failure is detected, the circuit turns on the floodlights. Many of these individual units need to be spaced about a large area in order to properly illuminate it in an emergency.
The Central Inverter System or CIS also includes a battery as well as charging and sensing circuits connected to the standard a.c. line. These circuits keep the battery charged and detect a power failure. However, the CIS also includes an inverter to convert d.c. power from batteries to a.c. power. Rather that supplying a single set of floodlights, the inverter output is supplied to dedicated emergency lighting circuits. These emergency circuits are wired to cause illumination of all exit signs and selected fluorescent and High Intensity Discharge ("HID") lamps. HID lamps include high pressure sodium and mercury vapor lamps.
In a typical office, the CIS is wired to power only one fluorescent and/or HID light in every five to ten throughout most of the facility. It would be cost prohibitive to supply emergency power to all fixtures as it would rapidly drain the batteries and provide lighting levels many times that required by code. Consequently, only a sufficient number of fluorescent and/or HID light fixtures are powered to provide the minimum light between fixtures that is required by code. Incandescent, electroluminescent or L.E.D. light sources are used at emergency exits and are generally required by law to be fully illuminated. Therefore, some areas in a work space, and all of the areas at exits, will be completely illuminated, while other areas will only be dimly lit.
A single CIS system is more desirable in larger lighting systems than hundreds of individual unit lights because it is more cost effective. However, since in those CIS systems known in the art only selected lighting fixtures are powered, a separate dedicated emergency wiring system must be installed. This can make initial or retrofit installations expensive.
Emergency lighting systems involving the application of high frequency input voltage are known in the art. For example, U.S. Pat. Nos. 3,836,815; 3,869,639; 4,477,748; 4,587,460; 4,686,424; 4,688,154 and U.S. Pat. No. 4,803,406 disclose lighting systems that involve the application of a high frequency input voltage. These systems use the high frequency input, typically several thousand cycles per second, for the purpose of increasing the efficiency and operating life of the lamps during either normal or emergency conditions. None of these known systems provides a means by which all of the lights in a facility are illuminated at a higher frequency only when there is a power failure.
The presence of some unilluminated areas in a facility represents a hazard to people trying to leave a work space during an emergency. It is an object of this invention to eliminate this hazard by providing uniform low level emergency lighting during a utility power failure.